As stated above, for 12 and 20 gauge you use the same loading data for the new as one does for the old. The only difference I have found is that I generally don't get more than 3 or 4 reloads before the cases randomly start buckling near the top of the base wad when crimping in my Hornady 391 Apex progressive. The older cases, being one-piece, were stronger at this point. This may not be a problem in a non-progressive reloader, such as the MEC 600 Jr.

Jim Haynes